Sacral spinal nerve 1

First sacral spinal nerve

The sacral spinal nerve 1, also known as S1, is the first of the five pairs of sacral nerves in the human body. These nerves are part of the peripheral nervous system and play a crucial role in the innervation of the lower limbs and pelvic organs.

Anatomy

The S1 nerve emerges from the spinal cord at the level of the first sacral vertebra. It exits the vertebral column through the sacral foramina, which are openings in the sacrum, a large, triangular bone at the base of the spine.

Course

The S1 nerve is part of the lumbosacral plexus, a network of nerves that supplies the lower limb. It combines with fibers from the lumbar spinal nerves and other sacral nerves to form the sciatic nerve, the largest nerve in the body. The sciatic nerve travels down the posterior aspect of the thigh, where it innervates muscles and skin.

Branches

The S1 nerve contributes to several important branches:

• The sciatic nerve, which innervates the posterior thigh muscles and all muscles below the knee.
• The superior gluteal nerve, which innervates the gluteus medius, gluteus minimus, and tensor fasciae latae muscles.
• The inferior gluteal nerve, which innervates the gluteus maximus muscle.

Function

The S1 nerve is responsible for motor and sensory functions in the lower limb. It provides motor innervation to muscles such as the gluteus maximus, which is involved in hip extension, and the gastrocnemius and soleus muscles, which are involved in plantarflexion of the foot. Sensory fibers from the S1 nerve supply the skin over the posterior aspect of the leg and the lateral aspect of the foot.

Clinical significance

Damage to the S1 nerve can result in weakness or paralysis of the muscles it innervates, leading to conditions such as foot drop or difficulty in walking. Sensory loss may occur in the areas supplied by the S1 nerve, leading to numbness or tingling sensations.

Also see

• Lumbosacral plexus
• Sciatic nerve
• Sacral plexus
• Peripheral nervous system

References

• Gray's Anatomy (1918), public domain text.
• Netter, Frank H. (2014). Atlas of Human Anatomy. Elsevier.